What will happen is that the motherboard or CPU(I cant think of which) may just see them as 1333Mhz as apposed to 1600MH which they are rated at.

AMD stock ram settings are usually 1333 MHz @ 9-9-9-(28-34). Add to that AMD do not use XMP Ram profiles, that is an Intel thing. So yes you will have to go into the BIOS and manually change the speed, and the timings.